Elephant trunks were once snorkels

Australian scientists have discovered new evidence that modern elephants evolved from an aquatic ancestor that used its trunk as an underwater snorkel.

Previous studies on anatomy and biochemistry had led zoologists to believe that elephants shared a common ancestor with sea cows - the group which includes dugongs and manatees.

Now the new studies on a rare series of foetuses taken from elephants killed in a culling operation in South Africa's Kruger National Park suggest this common ancestor was in fact aquatic.

The most compelling evidence was that the six foetuses and one embryo, which ranged in age from 58 to 166 days, all contained a structure called a nephrostome, said Ann Gaeth, who carried out the research for her PhD at Melbourne University, under the supervision of Professor Marilyn Renfree and Dr Roger Short.

Nephrostomes, funnel-shaped kidney ducts, are found in freshwater fish and frogs as well as in the first developmental stages of certain egg-laying reptiles and egg-laying mammals (both of which lay their eggs in water). They have never before been recorded in any other mammals that give birth to live offspring.

Since structures appearing early in embryo development tend to be ancestral, this suggests elephants' early ancestors would probably have used their trunks as snorkels - a practice some modern elephants still follow if required to travel long distances across water.

Professor Renfree told The Lab the early elephants may have used their trunks to graze on sea grasses - as modern manatees and dugongs do with their "mini-trunks" - and then discovered the handy snorkelling possibilities, or it may have happened the other way around.

Other features which lend support to the notion of aquatic ancestry include the arrangement of the embryonic respiratory system and the fact the testicles are internal, a pattern shared by seals and whales but not followed by other land-living mammals.

Fossil evidence suggests elephants left behind their aquatic life about 30 million years ago, after evolving features that enabled them to adapt to life on land.

Such features included lungs that allow elephants to drink by sucking up a large amount of water in their trunks and hold it there before letting it gush into their mouths.

In their aquatic environment, a trunk was not needed for drinking as the elephants could much more easily drink directly through their mouths.